Closure member for electric discharge tubes and the like



R. M. BOWIE Nov. 7, 1939.

CLOSURE MEMBER FOR ELECTRIC DISCHARGE TUBES AND THE LIKE Filed March 31,1937 INVENTOR ATTORNEY Patented Nov. 7, 1939 PATENT, OFFICE CLOSUREIMEMBEB. FOR ELECTRIC DIS- CHARGE TUBES AND THE LIKE Robert M. Bowie,St. Marys, Pa., assignor to Hygrade Sylvania Corporation, Salem, Mass,a. corporation of Massachusetts Application March 31, 1937, Serial No.134,059

4 Claims. (01. 250-164) This invention relates to closures for electricdischarge tubes and more particularly to such devices of the vacuum orlow pressure type.

, The invention is in the nature of an improvement on the type ofclosure member disclosed in application Serial No. 82,742, filed June 1,1936.

A principal object of the invention is to provide an electron dischargetube of the composite metal-glass evacuated envelope type having avitreous window or closure member which is supported around itsperiphery against atmospheric pressure, by a member which is not sealedinto the said vitreous member.

A feature of the invention relates to an evacuated envelope having itsmain body portion of metal which is sealed to a vitreous closure memberby an intermediate ring or frame of metal, a portion of the envelopebeing provided with a peripheral seat or ridge to support the vitreousmember against atmospheric pressure without affecting the eflicacy ofthe seal.

Another feature relates to the means for supporting a metal-framedvitreous closure member for the metal wall of an evacuated enclosingenvelope, so that the frame can be welded or otherwise fastened to themetal wall without damaging the seal between the frame and the vitreousmember.

A further feature relates to an evacuated envelope having a main bodyportion of metal with a relatively massive vitreous member at the end,the arrangement being such that the mechanical supporting of thevitreous member against atmospheric pressure is borne substantiallyentirely by end thrust of the vitreous member directly against the endof the envelope. As a result of this feature the sealing ring or frameis used substantially entirely to eifect a vacuum tight seal between thevitreous member and the metal envelope and therefore it may be ofrelatively thin metal strip. Since the sealing strip must be of aspecial alloy the cost thereof is materially reduced while at the sametime enabling a more reliable and satisfactory seal to be achieved. Theuse of such thin metal strip for the sealing ring or frame has thepronounced advantage that if the vitreous member is sealed thereto by apress molding operation, as described for example in said applicationSerial No. 82,742, there is less chance of a defective seal existingthan is the case where the frame is of relatively heavy gauge sheetmetal stock.

A still further feature relates to an improved cathode ray tube of thecomposite metal-glass env p p While the invention will be describedherein as applied to a cathode ray tube such as is employed intelevision and similar receiving sys-- tems, it will be understood thatthe invention is equally well applicable to similar devices such asradio tubes, light sensitive devices, oscillograph tubes for televisionor picture analysis, for example tubes known in theart as iconoscopes",dissector tubes and the like. In fact the invention is applicable to anyevacuated device in which a vitreous closure member of large surfaceextent is required to be sealed in a vacuum tight manner to an enclosingenvelope. Furthermore, merely for purposes of explanation, the inventionwill be disclosed as embodied in a cathode ray tube of the rectangularend or window type, but it will be obvious that it is applicable toother shapes such as round, oval or the like. It will be understood thatwhile the invention is illustrated in connection with a device having awindow at one end thereof, this window may be located at any other partof the device, for example in one of the side walls. Likewise onlysufficient parts of the cathode ray tube structure are shown to enablethe invention to be understood. Accordingly in the drawing,

Fig. 1 is a longitudinal plan view, partly in section, of a cathode raytube embodying the invention.

Fig. 2 is a left-hand end view of Fig. 1.

Fig. 3 is a sectional view of Fig. 1 taken along the line 3-3 thereofand viewed in the direction of the arrows.

Fig. 4 shows a modification of the invention.

Fig. 5 is another view of the modification of Fig. 4.

Fig. 6 shows the invention embodied in a radio tube of the metalenvelope type.

Fig. 7 is a modification of Fig. 6.

Referring to Fig. 1, there is shown partly in section and partly indotted outline, a typical cathode ray tube comprising an elongated neckportion I of glass or other suitable material. The main body 2 of thetube is in the form of a frustum of a cone of a suitable metal such forexample as steel. In order to insure a vacuumtight seal between theportions I and 2 there is provided a special sealing ring 3 of an alloywhich has substantially the same coefiicient of expansion as the glassI. Preferably the flare 4 of the neck is of Coming 705AJ" glass and thering 3 is of kovar, an alloy consisting of approximately 18% cobalt, 28%nickel and 54% iron. While any known manner of effecting the unionbetween members 3 and 4 may be emdeflecting means are also provided. Fora detailed description of a typical electrode structure reference may behad to' application Serial No. 95,970, filed August 14, 1936. r

As shown clearly in Fig. l, the metal portion 2 is welded or otherwisehermetically" fastened to the ring I, and said body'portion'terminatesat its enlarged open end in aflange comprising a shoulder 5 and a rim 8,the latter prefer- I ably, although not necessarily, extending at rightangles to the longitudinal axis of the tube. The enlarged end of thetube body 2 is closed by means of a relatively :massive rectangulartransparent vitreous member I of such dimensions that it fits snugly inthe shoulder. 6, and for this purpose preferably the said member'l isprovided with a rim 8 where it contacts with the shoulder 5.

In order. to provide a vacuum-tight seal between the closure member andthe tube proper the said closure member has sealed into and 1 around theedge thereof .ametal frame 9 having an integral flat rim ll joinedthereto by a curved portion H. The rim 10 preferably extends parallel tothe member I and is di" oned so that when the rim 8 is in'contact withshoulder 5,

the parts 6 and III are likewise in contact. In

other words, the weight of the member I is borne substantially entirelyby the shoulder i. It will be understood of course that the innersurface of member I is provided with a suitable coating of material ormaterials which become fluorescent when struck by the electron beam,asindicated by the stippling in Fig. 3. When the member I has beenpositioned on the end of the tube the parts 6 and Ill may behermetically sealed as by welding, brazing and the like and thereafterthe tube may be evacuated and processed in the manner well-known in theelectron tube art.

I have found that with the particular manner of supporting the member 1as described, it is possible to use relatively thin metal strip stockfor the frame 9 since this frame is employed merely to provide a vacuumtight seal between the rim 6 and the glass 1. Heretofore it has beenproposed to employ relatively heavy gauge metal sheet for the frame 9since this frame was required not only to effect the necessaryvacuumtight seal but also to carry the entire weight of the member I andalso the force of the atmospheric pressure on said member. Apart fromthe difficulty of welding a relatively massive metal frame to the rim 6,there was always the possibility that during the welding of the parts 8and ill, the seal between the glass 1 and the frame 9- might bedestroyed. I have found that the use of light gauge metal strip for theframe as is rendered possible by the present disclosure, not onlyfacilitates the welding of the parts 6 and ill but also reduces thechance of destroying the seal.

In addition to the advantages of providing a more reliable seal is theeconomic advantage that considerably less material is required for theframe 9. When it is considered that a special alloy must be used for thesaid frame it a once fective seals and defective windows.

duces the cost of the finished tube. For example with the arrangement asdescribed I have fcund it possible to employ for the frame 9, kovar ofthe order of 0.0075 inch in thickness, whereas to produce a satisfactoryseal with the prior method it was necessary to use an alloy of the orderof 0.03 inch in thickness.

In addition to improving the seal and reducing the cost of assembling.the tube. the use of the thin gauge metal frame also reduces the cost of'sealing'in the said-frame tothe glass 1. This is particularly truewhere the frame 9 is sealed into the glass 1 by apressure moldingoperation such for example as disclosed in said application SerialNo.'82,742. When relatively heavy gauge metal strip is employed in theframe, as a result of the scaling in process it is necessary carefullyto anneal the frame and the seal area so as to avoid warping of theglass due possibly to slight differences in-the. rates of cooling of theglass and metal, or to avoid distortion of the frame. This annealingoperation not only increased the cost .and time; of manufacturing theframed' window, but also increased'the percentage of de- I have foundthat by mechanically supporting the window on the shoulder 5,againsthtmospheric, pressure, enabling theuse of the thin gauge metalfor the frame, the costly annealing operation referred tois obviated orat least the same degree of care and-control is not necessary whensealing the frame 9 into the glass I. The above noted disadvantages ofthe prior tubes made with heavy gauge metal for the frame 9 areparticularly noticeable when the window is non-circular in shape.Forexample in the case of rectangular windows as shown in the drawing,the use of heavy gauge metal for the frame very frequently caused theglass to crack, particularly at the corners, during the seam welding ofthe parts 6 and I0. If with the prior construction the frame 9 were madesufllciently thin to avoid this cracking during the seam welding, itwould then be too thin to support the window against the atmosphericpressure on the outside thereof.

Preferably, in order to avoid trapping of air between the contactingsurfaces of the rim 8 and shoulder 5 during the evacuation of the tube,the said rim 9 is provided with one or more grooves II. It will beobvious however that instead of providing these grooves in the rim 9,the shoulder 5 where it contacts with the rim Smay be grooved orcorrugated to avoid this trapping of air.

While the drawing shows the window I supported on the shoulder 5throughout its entire periphery, it will be understood that this is notnecessary. Thus there is shown in Figs. 4 and 5 an arrangement whereinthe window I is spaced throughout the major portion of its peripheryfrom the shoulder 5. In this embodiment the corners of the shoulder 5are provided, with projections l3 such for example as embossings or thelike, to engage and support the window 1. With the arrangement of Fig.4, therefore the window is out of contact with the member 2 except atthe points of support l3. Instead of providing the spacing andsupporting lugs on the shoulder 5, these lugs may be formed as integralprojections from the corners of the glass 1. Various other manners ofsupporting the window against the end of the tube portion 2 will beclear from the foregoing descriptions of typical embodiments.

While the invention has been described as applied to cathode ray tubesit is also applicable to 30 rim '1.

electron discharge tubes such as radio tubes, light-sensitive cells, andthe like. Thus there is shown in Fig. 6 a typical radio tube comprisingan enclosing envelope l5 of a metal such as steel 5 or other metalordinarily employed in metal radio tubes. The envelope I5 is providedwith a flange comprising the'shoulder l6 and the flat rim I1. Adapted tobe seated against the shoulder I6 is a closure member l8 of glass orother 10 suitable insulating material such as ceramic or the like andinto which are sealed in a vacuumtight manner the wire prongs l9-Suitably supported from the member l8 and within the envelope I5 is anywell-known form of radio tube mount indicated generally by the numeral20,

it being understood that this mount may be insulatingly spaced at itsupper end from the metal wall Hi. In order to seal the member l8 to themember 15 in a vacuum-tight manner, the said member I 8 has sealedtherein around the edge thereof a thin metal ring or frame 2|corresponding to the frame 9 of Fig. 1, it being understood that thering 2| is of a suitable metal capable of being sealed in a vacuum-tightmanner to the member I8, and having substantially the same coefficientof expansion as said member Ill. The member l8 carrying the ring 2| andthe electrode mount is assembled against the end of tube I5 and the flatrim 22 is seam welded to the The tube may thereupon be evacuated throughthe exhaust tubulation in the wellknown manner, after which thistubulation may be sealed off as indicated by the numeral 23.

Instead of providing the rims I! and 22 ex- 5 tending outwardlyrelatively to the vertical axis of the tube, these rims may be turneddownwardly as indicated in Fig. 7. Various changes and modifications maybe made without departing from the spirit and scope of the invention. Bythe expression "permanently evacuated" as employed in the claims ismeant a device such as a cathode-ray tube which has been evacuated andhas been permanently sealed-oi, to distinguish from an arrangement wherethe parts are not 5 sealed together in a vacuum-tight manner and requireevacuation during the operation of the device.

What I claim is:

1. An electron discharge tube having a body portion in the form of ametal tube, a flange at the end of said body portion defining aperipheral seat, a vitreous closure member for said tube said closuremember being supported from said 5 flange by a plurality of spacedprojections, a metal frame sealed in a vacuum-tight manner into andaround said closure member, said frame being fastened to the end of saidtube in a vacuum-tight manner. 10

2. A cathode ray tube having a glass neck joined to a flared metaltubular member, a vitreous plate closing off the enlarged end of saidtubular member, a peripheral shoulder in said enlarged end to receivesaid plate, a thin metal 15 frame sealed into and around the edge ofsaid plate, said frame being welded to the flared end of said tubularmember.

3. A cathode ray tube comprising a glass neck sealed to a flared metalbody portion, a flange at 20 the end of said body portion and extendingsubstantially perpendicularly to the axis thereof, a peripheral seat insaid flange, a relatively massive vitreous plate conforming in shape tosaid seat and lying thereon, a thin metal frame sealed 25 into the edgeof said plate and having a flange extending parallel to thefirst-mentioned flange, both of said flanges being fastened together ina vacuum-tight manner.

4. An electron discharge tube having a metal tubular body portion, aperipheral flange at one end of said body portion and provided with aperipheral shouldered recess, an insulating closure member in the formof a substantially flat glass member lying in said recess, said recessreceiving substantially the entire thrust of said glass memberunderoutside atmospheric pressure, a plurality of lead-in wires sealeddirectly through said glass member, an electrode mount supported fromsaid closure member within said tubular body, a thin metal frame havingone peripheral margin sealed directly in a vacuumtight manner into andaround the margin of said glass member and its other peripheral marginsealed directly to the peripheral flange on a said body portion.

ROBERT M. BOWIE.

